1) Which LNB should be dead center and which one will be offset?
The Ku band LNB should be at the center of the dish (the correct focal point) because its wave length and focal point is smaller than it is for C-Band.
This is why you have to be more careful when aligning a Ku band dish vs. a C-Band dish.
If you put the C-Band LNB in the center and the Ku-Band LNB on the side you will lose a lot of signal quality on the Ku-Band (A 1.2 Meter dish will seem like a 36" - 39" dish)
and you will not gain that much on the C-Band signal (The slight gain might be helpful on borderline transponders).
Band Frequency Wavelength
Middle of C-Band - 3.95 GHz - 3.00 inches
Middle of Ku-Band - 11.95 GHz - 0.99 inches
2) How far apart does the offset have to be from the center LNB, and does it matter if the offset is left or right of the center LNB?
The closer the offset LNB is to the correct focal point of the dish, The stronger the signal quality will be. Also the further away from the correct focal point the LNB is placed,
the less surface area the LNB will see, so you reduce the effective size of the dish seen by the LNB (Lower signal quality).
If the offset LNB is on the right side of the real focal point then the dish has to be pointed more west to pick up a satellite,
and if the offset LNB is on the left side of the dish then the dish will have to be pointed more east to pick up a satellite.
The reason why I decided to place the C-Band LNB on the right side is because where it is positioned it is offset by about 5.5° West
So if I want to pick up C-Band on my furthest Eastern satellite (55.5° west) I need my motor to point at 50.0° West and it can not.
The furthest I can point my dish to is 53° West. With the LNB on the right side I need to point at 61.0° West which my motor can do.
3) Is it always advisable to cut the C-Band Scalar like this picture by QWERT1515 or can KU LNB be placed just next to the realm of the C-Band Scalar without cutting it?
The reason I cut the scalar was to allow the Ku band LNB to be able to see the whole dish and have the C-Band LNB as close to the real focal point as possible.
(This gives the highest signal quality for an offset LNB).